A pointing device is typically used for controlling the position of a cursor or pointer on a display, such as a computer display. For desktop personal computers (PC's), a commonly used pointing device is the “mouse”. A mouse is a hand held object that is moved over a flat surface near the keyboard to control the motion of a cursor on the computer display. The direction and distance over which the mouse is moved determines the direction and distance the cursor moves on the display.
While the mouse has provided a satisfactory solution to the pointing device problem in the desktop PC market, a similarly successful device is not available for portable and hand-held computers, and other portable electronic devices. For portable electronic devices, such as laptop computers, cellular telephones, personal digital assistants (PDAs), digital cameras, portable game devices, pagers, portable music players (e.g., MP3 players), and other devices, it may be undesirable to use an external pointing device, such as a mechanical mouse or an optical mouse, coupled to the device. It is often inconvenient to carry around the additional equipment, and these portable electronic devices are often used in environments that lack a sufficiently large flat surface over which a mouse can be moved.
Currently, there are two dominant solutions to the pointing device problem in the laptop marketplace, which are the Synaptics capacitive TouchPad™ and the IBM TrackPoint™. Other companies make versions of these devices with similar functionality. The TrackPoint™ is a small button that is typically placed in the center of the laptop keyboard. The button may be moved in a manner analogous to a “joy stick” by applying a lateral force to the top of the button with a finger. Unfortunately, the button can only move a small amount; hence, the displacement of the button cannot be mapped directly into a displacement in the cursor position on the computer display. Instead, the button displacement controls the direction and speed with which the cursor moves. The accuracy with which a user can position the cursor using this type of velocity control is significantly less than that achieved with a conventional mouse. This limitation is particularly evident in tasks that require small, precise movements such as drawing in a computer graphics program.
The TouchPad™ is a blank rectangular pad, typically 50-100 mm on a side, and typically placed in front of the keyboard of most laptops. The device senses the position of a finger on the surface of the rectangle relative to the edges of the device. This sensing is accomplished by measuring the capacitance changes introduced by a user's finger on a series of electrodes beneath an insulating, low-friction material. Like the TrackPoint™, the TouchPad™ also suffers from lack of precision. It is inherently difficult to measure the capacitive changes introduced by the user, who is at an unknown potential relative to the circuit. Furthermore, the contact area of the user's finger is relatively large. To provide an accurate measurement of the finger position, the device typically determines some parameter such as the center of the contact area between the finger and the pad. Unfortunately, the contact area varies in size and shape with the pressure applied by the user. Therefore, such determinations are, at best, of limited precision. In practice, users are unable to repeatably execute precise movements. There are also difficulties arising from false signals when the user inadvertently touches the pad with a finger or a wrist.
Some portable electronic devices include indicators, such as blinking lights or audible indicators, to provide some type of notification to a user, such as a notification that the user has received an email message or voicemail message. For example, some telephones include a blinking light to notify the user that the user has received a voicemail message. Such indicators are typically provided by a stand-alone light-emitting diode (LED) on the device, on a display screen of the device, or by an audio subsystem, and are not typically incorporated into a pointing device.